Planet Earth teems with life. However, not all of the world is particularly friendly to its inhabitants for this is also planet of extremes: blistering deserts, barren mountain peaks, bleak ley wastelands and dark places that rarely see the sun. In the freezing world of the Arctic, the polar bear is equipped with a coat of fur and blubber designed to cope in a land where winters seem interminable . Mountain goats need to cope with thin air and treacherous terrain found above the snow line. Life in the desert is a constant battle against a lack of water. The saguaro cactus can expand sufficiently to absorb a ton of water a day when the rains come. In the deepest, darkest caves, freetail bats have developed extraordinarily sensitive hearing . Finally, in the mysterious deep of our oceans, fragile jellyfish are gelatinous enough to thrive in water pressure that would crush most creatures.